1. Field of the Invention
The present invention relates to an image-forming medium, coated with a layer of microcapsules filled with dye, on which an image is formed on the microcapsule layer by selectively breaking and rupturing the microcapsules in the microcapsule layer.
2. Description of the Related Art
In a conventional type of image-forming medium coated with a layer of microcapsules filled with dye or ink, a shell wall of each microcapsule is formed from a suitable photo-setting resin, and an optical image is recorded and formed as a latent image on the microcapsule layer by exposing it to light rays in accordance with image-pixel signals. Then, the latent image is developed by exerting a pressure on the microcapsule layer. Namely, the microcapsules, which are not exposed to the light rays, are broken, whereby the dye or ink is discharged from the broken microcapsules, and thus the latent image is developed by the discharged dye or ink.
Thus, the conventional image-forming medium must be packed so as to be protected from being exposed to light, resulting in a wastage of packing materials. Further, the image-forming medium must be handled such that they are not subjected to excess pressure due to the softness of unexposed microcapsules, resulting in an undesired discharging of the dye or ink
Also, another type of image-forming medium, coated with a layer of microcapsules filled with different color dyes or inks based on diazo pigment, is known. The respective different color dyes or inks are transparent at normal ambient temperature, but each ink develops a monochromatic color at a specific temperature. Thus, the respective different colors are selectively developed on the microcapsule layer by selectively applying specific temperatures to the microcapsule layer. It is then necessary to fix the developed color by irradiation, using a light of a specific wavelength. Accordingly, this type of color-image-forming system is costly, because an additional irradiation apparatus for fixing the developed color is needed, and electric power consumption is increased due to the additional irradiation apparatus. Also, since a heating process for the color development and an irradiation process for fixing a developed color must be carried out with respect to each color, this hinders the quick formation of a color image on the image-forming medium.
Therefore, an object of the present invention is to provide an image-forming medium coated with a layer of microcapsules filled with ink or dye, in which an image can be quickly formed on the microcapsule layer at low cost without a large amount of wastage of packing materials, and which can be handled without special care.
In accordance with a first aspect of the present invention, there is provided an image-forming medium comprising a substrate, and a layer of microcapsules, coated over the substrate, composed of a binder material and a plurality of microcapsules filled with a dye and uniformly distributed in the binder material. The binder material exhibits a predetermined thermal melting point, and the microcapsules exhibit a pressure-breaking characteristic so as to be squashed and broken under a predetermined pressure when the binder material is thermally softened or melted.
The binder material may comprise either a wax material exhibiting the thermal melting point or a low-melting thermoplastic material exhibiting the thermal melting point. Preferably, the binder material comprises a plurality of binder particles which are adhered to each other such that a rockwork-like structure is given to the microcapsule layer.
The microcapsule may further include a vehicle and a dye or compound dispersed or dissolved in the vehicle. When the compound comprises a leuco-dye or leuco-compound, the binder material contains a color developer for the leuco-dye or leuco-compound.
The microcapsules may have a shell wall formed of a heat resistant synthetic resin which preferably comprises either a thermosetting resin or a high-melting thermoplastic resin.
Optionally, the dye may comprise a leuco-compound-based dye. In this case, the binder material comprises a color developer for the leuco-compound-based dye. Preferably, the color developer comprises a plurality of color developer particles which are adhered to each other such that a rockwork-like structure is given to the microcapsule layer. The microcapsule layer may contain a sensitizer for facilitating a color-developing reaction of the leuco-compound-based dye with the color developer.
In accordance with a second aspect of the present invention, there is provided an image-forming medium comprising a substrate, and a layer of microcapsules, coated over the substrate, including first and second microcapsule layer sections. The second microcapsule layer section is formed on the substrate, and the first microcapsule layer section is formed on the second microcapsule layer section. The first microcapsule layer section is composed of a first binder material, and a first type of microcapsules filled with a first dye and uniformly distributed in the first binder material, and the second microcapsule layer section is composed of a second binder material, and a second type of microcapsules filled with a second dye and uniformly distributed in the second binder material. The first binder material exhibits a first predetermined thermal melting point, and the first type of microcapsules exhibits a first pressure-breaking characteristic so as to be squashed and broken under a first predetermined pressure when the first binder material is thermally softened or melted. The second binder -material exhibits a second predetermined thermal melting point higher than the first thermal melting point, and the second type of microcapsules exhibits a second pressure-breaking characteristic so as to be squashed and broken under a second predetermined pressure lower than the first predetermined pressure when the second binder material is thermally softened or melted.
In the image-forming medium according to the second aspect of the present invention, the microcapsule layer may further include a third microcapsule layer section intervened between the substrate and the second microcapsule layer section. The third microcapsule layer section is composed of a third binder material, and a third type of microcapsules filled with a third dye and uniformly distributed in the third binder material, and the third binder material exhibits a third predetermined thermal melting point higher than the second thermal melting point, the third type of microcapsules exhibiting a third pressure-breaking characteristic so as to be squashed and broken under a third predetermined pressure lower than the second predetermined pressure when the third binder material is thermally softened or melted.
Preferably, an average diameter of the first type of microcapsules is smaller than an average diameter of the second type of microcapsules, and an average diameter of the second type of microcapsules is smaller than an average diameter of the third type of microcapsules.
The first microcapsule layer section may include a first type of spacer particles uniformly distributed therein and having an average diameter larger than an average diameter of the first type of microcapsules, and the second microcapsule layer section may include a second type of spacer particles uniformly distributed therein and having an average diameter larger than an average diameter of the second type of microcapsules. The spacer particles may be formed of an inorganic material. Optionally, the spacer particles may be formed of a high-melting synthetic resin.
Preferably, each of the first, second and third binder materials comprises a plurality of binder particles which are adhered to each other such that a rockwork-like structure is given to a corresponding microcapsule layer section.
Each of the first, second and third microcapsules may include a vehicle and a dye or compound dispersed or dissolved in the vehicle. When the dye or compound comprises a leuco-dye or leuco-compound, a color developer for the leuco-dye or leuco-compound is contained in a corresponding microcapsule layer section.
Optionally, the respective first, second and third dyes may comprise first, second and third leuco-compound-based dyes. In this case, the respective first, second and third binder materials comprise first, second and third color developers for the leuco-compound-based dyes. Preferably, each of the first and second color developers comprises a plurality of color developer particles which are adhered to each other such that a rockwork-like structure is given to a corresponding microcapsule layer section. Each of the first, second and third microcapsule layer sections may contain a sensitizer for facilitating a color-developing reaction of a corresponding leuco-compound-based dye with a corresponding color developer.
In accordance with a third aspect of the present invention, there is provided an image-forming medium comprising a substrate, and a layer of microcapsules, coated over the substrate, composed of a color developer, a first type of microcapsules filled with a first leuco-compound-based dye and uniformly distributed in the color developer, and a second type of microcapsules filled with a second leuco-compound-based dye and uniformly distributed in the color developer, the color developer exhibiting a predetermined thermal melting point. The first type of microcapsules exhibits a first pressure-breaking characteristic so as to be squashed and broken under a first predetermined temperature higher than the predetermined thermal melting point and a first predetermined pressure when the color developer is thermally softened or melted. The second type of microcapsules exhibits a second pressure-breaking characteristic so as to be squashed and broken under a second predetermined temperature higher than the first predetermined temperature and a second predetermined pressure lower than the first predetermined pressure when the color developer is thermally softened or melted.
Preferably, the second type of microcapsules has a double-shell-wall structure composed of an inner shell wall section and an outer shell wall section, one of which is thermally softened or melted under the second predetermined temperature.
Preferably, an average diameter of the first type of microcapsules is smaller than an average diameter of the second type of microcapsules, and the microcapsule layer includes a plurality of spacer particles having an average diameter larger than the average diameter of the first type of microcapsules but smaller than the average diameter of the second microcapsules.
Preferably, the color developer comprises a plurality of color developer particles which are adhered to each other such that a rockwork-like structure is given to the microcapsule layer.
The microcapsule layer may contain a sensitizer for facilitating a color-developing reaction of each leuco-compound-based dye with the color developer.